The invention relates to the design of projection screens, in particular of projection screens of a type that allow simultaneous reproduction of sound.
Presently, essentially two different types of projection screens exist: rear projection screens and front projection screens. With rear projection screens, the image is produced on the side of the projection screen facing away from the spectator. This projection method is known, for example, from television picture tubes.
With front projection screens, the image is produced on the side of the projection screen facing the spectator, whereby the images to be reproduced are projected on to the projection plane from a projector placed at a distance from the projection screen. This method, which also forms the subject matter of the present invention, is known, for example, from movie theaters and slide projection. The latter (front) projection screens have a relatively large size as compared to the rear projection screens described first. Movie theaters, for example, typically employ projection screens having a projection screen diagonal in excess of 15 meters.
If sound effects are to be reproduced in addition to the visual effects, then both projection methods rely on conventional loudspeaker technology, wherein respective loudspeakers or loudspeaker boxes are arranged along the periphery of the respective projection screen. This device is necessary in order to convey to a spectator the impression that the respective sound events originate from the events displayed on the projection screen or are at least related to these events.
To provide an adequate audio level for the room in front of large format projection screens, a large number of conventional loudspeakers of suitable signs should be provided. However, such sound-producing devices can achieve excellent sound reproduction with setups having relatively small projection walls only if the space and/or area used for sound reproduction is disproportionately large relative to the size of the projection screen and/or the size of the image. This is less of an issue with relatively large projection screens. However, with projection screens having a large image diagonal, the audio effects can be noticeably misaligned relative to the visual effects, when the sound reproducing device is placed along the sides of the projection screen. Conversely, while placing the sound reproducing system behind the projection screen improves the mutual correlation between visual and audio effects for large projection screens, the projection screen can disadvantageously interfere with the reproduction of the high frequencies.
For example, U.S. Pat. No. 5,025,474A discloses a projection screen consisting of several segments of which at least some segments operate as sound radiating elements for radiating sound waves from the projection plane of the projection screen. Similar projection screens are described also in U.S. Pat. No. 1,817,630 A, GB 353 439 A, EP 0 323 110 A and U.S. Pat. No. 5,007,707 A. However, these arrangements still do not adequately reproduce high frequencies.
It is therefore an object of the invention to provide a projection screen which eliminates the disadvantages in the sound reproduction associated with the aforementioned conventional devices.
A very compact and space-saving device for simultaneous transmission of visual and audio effects includes a projection wall with at least one segment that radiates sound waves out of the projection plane of the projection screen. With this device, the required area and/or space is no greater than the size of the respective projection screen; in addition, the visual and audio events are once more combined in a single plane and completely and correctly associated with each other.
This is achieved by designing the sound reproduction segments of a projection screen with a different depth perpendicular to the projection plane in order to optimize the reproduction of certain frequency ranges.
The tonal response is optimized by using the entire area for sound reproduction. The higher frequencies are also no longer attenuated by the screen located in front of the loudspeakers.
If, the respective edges of the segments of the projection wall can be mutually decoupled by connecting elements, so that optimally formed sound reproduction segments for reproducing certain frequency ranges can be integrated in the same projection screen and, in addition, regions or zones can be created for transmitting, for example, the different channel information in stereo.
A particularly simple decoupled connection between the segments can be obtained if the segments are made of a core layer and at least one cover layer. The segments of the cover layer(s) and the core layer can then be connected in a simple manner by having the respective cover layer and/or the core layer also bridge the radial gaps between adjacent segments. In particular, by using the core layer to connect several segments, relatively large sections of the core layer can advantageously be manufactured as a continuous uniform piece before the segments produced from this piece are decoupled through cutouts or milled-out portions in the core layer.
The segments and/or sound radiating segments integrated in a projection screen do not necessarily require an area of uniform size in the projection plane of the projection screen. Instead, these areas can be designed and associated with each other to provide flexibility in the sound reproduction of the projection screen.
The bass reproduction can be significantly improved by arranging the segments that are optimized for reproducing low frequencies primarily in the central region of the projection screen, because those segments and/or portions of the projection screen that laterally abut the segments provided for the bass transmission, can be used to reduce dipole shunting.
The sound reproduction can be further optimized by optimizing the sound production segments of a projection screen that are designed to reproduce certain frequency ranges, by giving them a different depth perpendicular to the projection plane.
The projection surface of the projection screen need not be planar, but can also be curved. This device modifies the radiated sound pattern, thereby further optimizing the sound generation for the room. Thexe2x80x94not necessarily uniformxe2x80x94curvature of the projection surface selectively addresses, for example, certain areas in the auditorium and hence can further improve the audio perception.